This invention relates to olefin polymerization catalysts and particularly relates to a prepolymerized supported alpha-olefin polymerization catalyst which has been temporarily deactivated before use.
Use of solid, transition metal-based, olefin polymerization catalyst components is well known in the art including such solid components supported on a metal oxide, halide or other salt such as widely-described magnesium-containing, titanium halide-based catalyst components. Also well known is prepolymerizing a solid catalyst component with a small amount of olefin before introducing such component into a main polymerization reactor. Typically, such prepolymerization reduces catalyst attrition and thereby improves the resulting polymer morphology. Also, it has been found that such prepolymerized solid catalyst component suspends more readily in hydrocarbons, yields polymers of higher bulk density, and reduces formation of strings and lumps in gas-phase polymerizations.
In a typical prepolymerization method, solid catalyst component is contacted in a suitable diluent with a small amount of olefin monomer in a vessel separate from a main polymerization reactor and in the presence of a cocatalyst such as an organoaluminum compound. After a small amount of polymer is formed around the solid catalyst particle, a slurry of the prepolymerized catalyst component is introduced into a main reactor. A problem arises in a solventless polymerization process, such as a bulk or gas-phase process, in which solid catalyst component is flushed into a main reactor with liquid monomer. If a solid catalyst component is prepolymerized for use in such solventless processes in the necessary presence of a cocatalyst, polymerization will continue in the liquid monomer catalyst flush or transfer lines and causes such lines to plug.
The problem of preventing unwanted polymerization in catalyst transfer lines is described in U.S. Pat. No. 4,130,699, in which an olefin, such as ethylene or propylene, polymerization catalyst component temporarily deactivated with an agent such as alcohols, sulfides, ethers, ketones, hydrogen sulfide, or hydrogen chloride and subsequently reactivated in a main reactor. However, this technique is a complex procedure and is not preferred for prepolymerized highly active, supported catalysts.
This invention is a prepolymerized supported olefin polymerization catalyst component which is temporarily inactivated so that it may be transferred to a polymerization reactor.